Method for controlling deformation of hollow structure diffusion welding

Abstract

The application provides a hollow structure diffusion welding deformation control method, and belongs to the technical field of welding. The method comprises the following steps: processing an inner cavity on a semi-finished product to be welded, and processing an outer cavity on the outer surface of the semi-finished product at a position corresponding to the inner cavity, the size of the outer cavity is smaller than the projection size of the corresponding inner cavity on the outer surface, and the depth of the outer cavity is 0.2mm-1mm; then, the surface to be welded is subjected to surface treatment; the two semi-finished products are assembled and aligned, and are arranged between the upper die and the lower die of a welding tool, and are placed into a vacuum diffusion welding furnace; vacuum is drawn, and vacuum diffusion welding is carried out according to a preset heating and pressurizing curve; after welding, final machining is carried out to remove the welding allowance and the outer cavity structure, and a finished product hollow component is obtained. The outer cavity is prefabricated before welding, the collapse deformation of the inner cavity area in the welding process is effectively compensated, the welding deformation amount is controllable, the conventional welding compression amount parameters can be used, the number of trial weldings is reduced, the product qualification rate and the production efficiency are improved, and the method is especially suitable for the manufacturing of aviation parts.

Description

Technical Field

[0001] This invention relates to the field of welding technology, and more specifically, to a method for controlling deformation during diffusion welding of hollow structures. Background Technology

[0002] Vacuum diffusion bonding (VDB) is an advanced welding process that achieves a metallurgical connection between two closely contacting solid metal surfaces by applying pressure and temperature in a vacuum environment, causing atomic diffusion. Because it produces little or no liquid phase during the welding process, it results in minimal weld deformation, high joint quality, and precise control of the weld interface. It is widely used in high-end manufacturing fields such as aerospace and nuclear energy, and is particularly suitable for welding reactive metals such as titanium alloys.

[0003] In the field of aero-engines, to reduce structural weight and improve thrust-to-weight ratio, hollow structure designs are increasingly being adopted for key rotating / stationary components such as fan blades and rectifier blades. These hollow components are typically formed by diffusion welding of two (or more) half-bulbs to create an internal cavity, followed by subsequent machining to achieve the final external dimensions. Using diffusion welding to manufacture hollow structural components can achieve significant weight reduction while maintaining structural strength, making it one of the important technological routes for lightweight aero-engine manufacturing.

[0004] Currently, the main manufacturing processes for hollow split junctions are brazing and diffusion welding. However, each of these processes has its own drawbacks and limitations, as detailed below: (1) Brazing can be used to manufacture the above-mentioned hollow split structure. However, the weld structure of brazing is different from that of the base material, and the joint strength is difficult to be equal to that of the base material, thus limiting the scope of application.

[0005] (2) Vacuum diffusion welding is a solid-state welding technology with high joint quality. However, it requires the material to undergo a certain plastic deformation during the diffusion welding process. The existing solution is usually to increase the allowance at the welding surface to offset the overall welding pressure. However, the deformation at the center of the cavity is not uniform with that at the edge of the cavity, so simply raising the welding surface will not meet the part requirements after welding.

[0006] Therefore, there is an urgent need for a simple, effective, and engineerable method for controlling deformation during hollow structure diffusion welding, which can actively compensate for deformation in the inner cavity region during welding, so that the outer surface of the welded part remains flat, thereby ensuring the uniformity of subsequent machining allowances and the final dimensional accuracy of the part. Summary of the Invention

[0007] (a) Technical problems to be solved The technical problem to be solved by the present invention is that the deformation of the outer surface is difficult to control during the diffusion welding process of hollow structures in the prior art, and the post-weld precision cannot meet the requirements of the parts.

[0008] (II) Technical Solution To achieve the above objectives, the technical solution adopted by the present invention is as follows: This invention provides a method for controlling deformation during diffusion welding of hollow structures, comprising the following steps: Step 1: Machining an inner cavity on the semi-finished workpiece to be welded, and simultaneously machining an outer cavity on the outer surface of the semi-finished workpiece at a position corresponding to the inner cavity. The size of the outer cavity is smaller than the size of the projection of the corresponding inner cavity onto the outer surface of the semi-finished workpiece, and the depth of the outer cavity is 0.2mm to 1mm. Step 2: Perform surface treatment on the surface of the semi-finished workpiece to be welded; Step 3: Align the two surface-treated half blanks, place them between the upper and lower molds of the welding fixture, and put the whole assembly into the vacuum diffusion welding furnace; Step 4: Evacuate the vacuum diffusion welding furnace and perform vacuum diffusion welding on the assembled semi-blank according to the preset heating and pressurization curve. The welding compression amount is set to the welding compression amount corresponding to the conventional non-open external cavity structure. Step 5: After welding is completed, the product undergoes final machining to remove welding allowance and external cavity structure, resulting in a finished hollow component.

[0009] Preferably, in step one, the shape of the outer cavity is similar to the shape of the inner cavity, and the projection of the outer cavity on the outer surface of the semi-finished workpiece falls completely within the contour range of the projection of the corresponding inner cavity on the outer surface.

[0010] Preferably, the depth of the outer cavity is 0.3 mm to 0.8 mm.

[0011] Preferably, in step two, the surface treatment involves cleaning the surface of the semi-finished workpiece to be welded using mechanical or chemical methods. This removes oxide films, oil stains, and other contaminants from the surface, improving the cleanliness and surface activity of the welding interface and promoting the diffusion and migration of interface atoms during the welding process.

[0012] Preferably, the mechanical method includes at least one of grinding, polishing, and sandblasting; the chemical method includes at least one of pickling and alkaline washing. In practice, appropriate surface treatment methods or combinations thereof can be selected based on the type of semi-finished part material, surface condition, and complexity of the internal cavity structure. For example, for titanium alloy semi-finished parts, sandblasting can be used first to remove the surface oxide layer, followed by pickling to further clean the surface to be welded; for applications requiring high surface roughness, a polishing process can be added after sandblasting or pickling.

[0013] Preferably, in step four, the welding compression amount is set to the welding compression amount corresponding to a conventional non-open external cavity structure. A conventional non-open external cavity structure refers to a welding compression amount determined by empirical formulas or experiments based on material properties, internal cavity dimensions, and welding process requirements, without machining an external cavity on the outer surface of the semi-finished part. Since this invention machines an external cavity structure on the outer surface of the semi-finished part, the deformation of the external cavity during welding will offset the deformation of the internal cavity, thereby slowing down or eliminating internal cavity deformation. Therefore, the same welding compression amount as a conventional solid / non-open external cavity structure can be used for welding, without needing to increase the compression amount due to the presence of an internal cavity, thus avoiding the problem of excessive deformation of the outer surface caused by excessive compression.

[0014] Preferably, in step five, the final machining includes the following steps: first, removing the excess material in the area where the outer cavity is located so that the outer surface reaches the design size, and then, according to the design requirements, finishing machining of the inner cavity and outer contour of the welded hollow component to the final size.

[0015] Preferably, the material of the semi-finished part is a titanium alloy, a high-temperature alloy, or an aluminum alloy. The titanium alloy may include commonly used aerospace titanium alloys such as TC4 (Ti-6Al-4V), TC11, TC17, and TC18; the high-temperature alloy may include nickel-based or cobalt-based high-temperature alloys such as GH4169 (Inconel 718), GH3030, and K465; and the aluminum alloy may include aerospace aluminum alloys such as 2A14, 7A04, and 7050.

[0016] (III) Beneficial Effects The above-described technical solution of the present invention has at least the following advantages: 1. This invention involves machining an outer cavity at a position corresponding to the inner cavity on the outer surface of a semi-finished part. The controlled plastic deformation of the outer cavity under welding pressure actively compensates for the surface collapse deformation of the inner cavity region. When welding pressure is applied to the semi-finished part, the outer cavity region preferentially undergoes plastic deformation due to the reduced wall thickness and stiffness. This deformation process precisely counteracts the surface collapse tendency of the corresponding inner cavity region caused by pressure concentration, thus ensuring a smooth outer surface of the welded part and significantly reducing deformation.

[0017] 2. Since the controllable deformation of the outer cavity compensates for the deformation of the inner cavity area, the present invention can use the same welding compression amount as the conventional non-open outer cavity (solid) structure for welding, without the need to increase the compression amount due to the existence of the inner cavity, which simplifies the process of determining welding process parameters and reduces the difficulty of process debugging and trial welding costs.

[0018] 3. The method of this invention only requires adding one external cavity processing step and one external cavity removal step to the existing diffusion welding process. It does not require major modifications to existing welding equipment and tooling, resulting in minimal process changes, low implementation costs, and easy application in industrial production. Furthermore, this invention is applicable to the diffusion welding of hollow structures made of various commonly used aerospace materials such as titanium alloys, high-temperature alloys, and aluminum alloys, and has broad engineering application prospects.

[0019] 4. Through the deformation compensation effect of the external cavity structure, the dimensional accuracy and surface quality of the welded parts are significantly improved, reducing the scrap of parts caused by welding deformation exceeding the tolerance, and significantly improving the product qualification rate and quality consistency, which is conducive to reducing manufacturing costs and improving production efficiency. Attached Figure Description

[0020] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0021] Figure 1 This is a schematic diagram of the structure of a semi-finished part provided in an embodiment of the present invention.

[0022] Figure 2 This is a schematic diagram of the structure after the two half blanks are assembled and aligned, as provided in an embodiment of the present invention.

[0023] Figure 3 This is a structural schematic diagram of the hollow component after welding, provided in an embodiment of the present invention.

[0024] The labels in the figures are explained as follows: 1. First half blank; 2. Second half blank; 3. Cavity; 4. Hollow component; 5. Final part shape; 11. First inner cavity; 12. First outer cavity; 21. Second inner cavity; 22. Second outer cavity. Detailed Implementation

[0025] To make the technical problems to be solved, the technical solutions, and the beneficial effects of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the present invention and are not intended to limit the present invention.

[0026] It should be noted that when a component is referred to as "fixed to" or "set on" another component, it can be located directly on or indirectly on the other component. When a component is referred to as "connected to" another component, it can be directly or indirectly connected to the other component.

[0027] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating relative importance or the number of technical features. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified. The specific implementation of this invention will be described in more detail below with reference to specific embodiments: This embodiment takes the manufacturing of hollow titanium alloy fan blades for aero-engines as an example to illustrate in detail the specific implementation process of the hollow structure diffusion welding deformation control method provided by the present invention.

[0028] like Figure 1 As shown, the hollow structure in this embodiment is formed by connecting a first half-blank 1 and a second half-blank 2 through vacuum diffusion welding. The first half-blank 1 has a first inner cavity 11 machined on its inner side, and a corresponding first outer cavity 12 machined on its outer surface; the second half-blank 2 has a second inner cavity 21 machined on its inner side, and a corresponding second outer cavity 22 machined on its outer surface. After welding, the first inner cavity 11 and the second inner cavity 21 together constitute the cavity 3 of the hollow component 4. The first outer cavity 12 and the second outer cavity 22 are used to compensate for the collapse deformation of the outer surface of the corresponding area of ​​the inner cavity through controllable plastic deformation during the welding process.

[0029] The specific implementation steps are as follows: Step 1: Using TC4 titanium alloy forged bars, the preliminary shapes of the first half-blade 1 and the second half-blade 2 are prepared by CNC milling. The first inner cavity 11 and the second inner cavity 21 are machined on the inner sides of the two half-blades, respectively. The shapes of the first inner cavity 11 and the second inner cavity 21 are consistent with the design shape of the internal cavity of the blade, with welding allowance and subsequent machining allowance reserved during machining. Simultaneously, the first outer cavity 12 and the second outer cavity 22 are machined by CNC milling at positions corresponding to the first inner cavity 11 and the second inner cavity 21 on the outer surfaces of the first half-blade 1 and the second half-blade 2, respectively. The shapes of the first outer cavity 12 and the second outer cavity 22 are similar to the shapes of the first inner cavity 11 and the second inner cavity 21, respectively (i.e., similar projected contour shapes). The projection of the first outer cavity 12 on the outer surface of the first half-blade 1 completely falls within the contour range of the projection of the first inner cavity 11 on the outer surface, and the projection of the second outer cavity 22 on the outer surface of the second half-blade 2 completely falls within the contour range of the projection of the second inner cavity 21 on the outer surface. The dimensions (area and outline length) of the first outer cavity 12 and the second outer cavity 22 are both smaller than the corresponding values ​​of the projected dimensions of the corresponding inner cavity on the outer surface, so as to ensure that the wall thickness of the outer cavity region is reduced but the structural rigidity is not excessively weakened.

[0030] Step 2: Perform surface treatment on the surfaces to be welded (i.e., the inner surfaces of the two half-blade pieces, including the inner cavity surface) of the first half-blade 1 and the second half-blade 2. Specifically, first, perform sandblasting to remove the oxide layer from the surfaces to be welded, ensuring the surface roughness meets the relevant requirements. Then, perform pickling on the sandblasted surfaces to further remove residual oxide film and contaminants. Finally, use anhydrous ethanol to ultrasonically clean the pickled surfaces to remove residual acid and other organic contaminants, and dry them before use.

[0031] Step 3: Assemble and align the surface-treated first half-blank 1 and second half-blank 2 using a dedicated positioning fixture, ensuring that the inner cavities of the two half-blanks are aligned and the interfaces to be welded are tightly fitted. After assembly, place the assembly between the upper and lower molds of the welding fixture, ensuring that the cavity contours of the upper and lower molds match the outer surface contours of the half-blanks. Subsequently, place the entire fixture along with the half-blank assembly into the vacuum diffusion welding furnace.

[0032] Step 4: Evacuate the vacuum diffusion welding furnace. When the vacuum level inside the furnace reaches the required level, begin vacuum diffusion welding according to the preset heating and pressurization curve. The welding compression is set to the compression level corresponding to conventional diffusion welding of TC4 titanium alloy with a non-open external cavity structure. During welding, the regions of the first external cavity 12 and the second external cavity 22, due to their reduced wall thickness and lower rigidity, preferentially undergo controllable plastic deformation under welding pressure. This plastic deformation precisely compensates for the collapse deformation tendency of the corresponding outer surfaces of the first inner cavity 11 and the second inner cavity 21, thus ensuring a smooth outer surface of the welded part.

[0033] Step 5: After welding, the hollow component 4 is cooled in the furnace to below the relevant process temperature before being removed from the furnace. The welded hollow component 4 is then subjected to final machining: First, the excess material in the area where the first outer cavity 12 and the second outer cavity 22 are located is removed by CNC milling so that the outer surface of the part meets the design size requirements; then, the inner cavity and outer contour of the welded hollow component 4 are precision machined to the final size according to the design requirements to obtain the finished hollow fan blade.

[0034] like Figure 2 As shown, after the first half-blade 1 and the second half-blade 2 are assembled and aligned, the first inner cavity 11 and the second inner cavity 21 together form the outline of the cavity 3. The first outer cavity 12 and the second outer cavity 22 are respectively located on the outer surfaces of the two half-blades and corresponding to the inner cavities. Figure 3 As shown, after welding, the first half blank 1 and the second half blank 2 are connected by diffusion welding to form a hollow component 4. After subsequent machining to remove the excess material in the outer cavity, the outer surface meets the design requirements of the final part shape 5.

[0035] This invention processes an outer cavity, smaller than the projected size of the inner cavity, on the outer surface of the semi-finished part at the position corresponding to the inner cavity. During the diffusion welding process, the rigidity of the outer cavity area decreases due to the thinning of the wall thickness. Under the action of welding pressure, controllable plastic deformation occurs preferentially. This amount of plastic deformation precisely compensates for the amount of outer surface collapse deformation caused by pressure concentration in the corresponding area of ​​the inner cavity, thereby keeping the outer surface of the welded part flat as a whole.

[0036] The range of the outer cavity depth (0.2mm to 1mm) was determined through extensive testing: when the outer cavity depth is less than 0.2mm, the wall thickness reduction in the outer cavity area is insufficient, the plastic deformation compensation effect is limited, and it cannot effectively offset the collapse deformation of the inner cavity area; when the outer cavity depth is greater than 1mm, the wall thickness of the outer cavity area is excessively thinned, and this area may undergo excessive deformation or even cracking during welding, thus introducing new defects. Setting the outer cavity size to be smaller than the corresponding inner cavity projection size on the outer surface ensures that the outer cavity area is completely within the inner cavity projection contour range, so that the plastic deformation compensation effect of the outer cavity accurately corresponds to the collapse deformation area of ​​the inner cavity area, avoiding unnecessary deformation introduced in non-corresponding areas due to the outer cavity exceeding the inner cavity projection range.

[0037] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for controlling deformation during diffusion welding of hollow structures, characterized in that, Includes the following steps: Step 1: Machining an inner cavity on the semi-finished workpiece to be welded, and simultaneously machining an outer cavity on the outer surface of the semi-finished workpiece at a position corresponding to the inner cavity. The size of the outer cavity is smaller than the size of the projection of the corresponding inner cavity onto the outer surface of the semi-finished workpiece, and the depth of the outer cavity is 0.2mm to 1mm. Step 2: Perform surface treatment on the surface of the semi-finished workpiece to be welded; Step 3: Align the two surface-treated half blanks, place them between the upper and lower molds of the welding fixture, and put the whole assembly into the vacuum diffusion welding furnace; Step 4: Evacuate the vacuum diffusion welding furnace and perform vacuum diffusion welding on the assembled semi-blank according to the preset heating and pressurization curve. The welding compression amount is set to the welding compression amount corresponding to the conventional non-open external cavity structure. Step 5: After welding is completed, the product undergoes final machining to remove welding allowance and external cavity structure, resulting in a finished hollow component.

2. The method for controlling deformation during diffusion welding of hollow structures as described in claim 1, characterized in that, In step one, the shape of the outer cavity is similar to that of the inner cavity, and the projection of the outer cavity onto the outer surface of the semi-finished workpiece falls completely within the contour range of the projection of the corresponding inner cavity onto the outer surface.

3. The method for controlling deformation during diffusion welding of hollow structures as described in claim 1, characterized in that, The depth of the outer cavity is 0.3mm to 0.8mm.

4. The method for controlling deformation during diffusion welding of hollow structures as described in claim 1, characterized in that, In step two, the surface treatment involves cleaning the surface of the semi-finished workpiece to be welded using mechanical or chemical methods.

5. The method for controlling deformation during diffusion welding of hollow structures as described in claim 4, characterized in that, The mechanical method includes at least one of grinding, polishing and sandblasting; the chemical method includes at least one of acid washing and alkaline washing.

6. The method for controlling deformation during diffusion welding of hollow structures as described in claim 1, characterized in that, In step four, the welding compression amount is set to the welding compression amount corresponding to a conventional non-open external cavity structure.

7. The method for controlling diffusion welding deformation of hollow structures as described in claim 1, characterized in that, Step five, the final machining process includes the following steps: First, remove the excess material in the area where the outer cavity is located to make the outer surface reach the design size. Then, according to the design requirements, the inner cavity and outer contour of the welded hollow component are precision machined to the final size.

8. The method for controlling deformation during diffusion welding of hollow structures as described in claim 1, characterized in that, The material of the semi-finished part is titanium alloy, high-temperature alloy or aluminum alloy.

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